Research has been carried out into two aspects of the cerebral circulation: (1) Its neurogenic control and (2) the basis of cerebral vasospasm. The response of cerebral blood vessels to electrical stimulation of intramural nerves has been studied in vitro. The constrictor response appears to be mediated by adrenergic-like mechanisms. The alpha-adrenergic receptor has unusual features, in that it is insensitive to the transmitter and does not react in the usual way with alpha-adrenergic blocking agents. The dilator response to nerve activation is not mediated by the sympathetic nervous system. The nature of the transmitter has yet to be established. An in vitro model of cerebral vasospasm has been studied. Stretch of the rabbit basilar artery results in small discrete tears of the internal elastic lamina associated with local constriction of the adjacent smooth muscle cells. These constrictions can be prevented by removing calcium from the environment and by the use of cyanide. Studies are under way to determine the basis of the prolonged local constriction.